Encapsulated electrical device

ABSTRACT

An electrical device includes two housing parts that may be joined to form one closed housing, the housing parts in the joined state enclosing a housing interior space, as well as an electrical/electronic circuit element arranged in the housing inner space, and a sealing material for protecting the circuit element. The two housing parts may be configured as half-shells and the interior area of the half-shells, in each case, may be subdivided by interior walls into at least two chambers, of which, in each case, a first chamber is filled with the sealing material and has spatial dimensions which are greater than the dimensions of the circuit element, the interior walls of the second half-shell, in the joined state of the two half-shells, overlapping the interior walls of the first half-shell with clearance, the interior walls of the first half-shell penetrating somewhat into the first chamber of the second half-shell, and the circuit element between the two half-shells being enveloped by the sealing material contained in the two first chambers, up to its electrical connections.

FIELD OF THE INVENTION

The present invention relates to an electrical device.

BACKGROUND INFORMATION

European Published Patent Application No. 0 722 624 describes anelectrical device which has a first and a second housing part, whichtogether form a closed housing. Arranged in the housing is a circuitelement that is configured as a printed-circuit board, supportingelements configured in the first housing part penetratingthrough-openings in the printed-circuit board. The support elements areconfigured so that the printed-circuit board moves in the direction ofthe first housing part when the second housing part is mounted, and asealing material, arranged between the printed-circuit board and thefirst housing part, is subjected to compression and is squeezed into aposition in which it forms a circumferential bulge on the side walls ofthe housing and as a result seals the contact area of the two housingparts. In the housing part that is sealed in this manner, a hollow spacefilled with air remains between the printed-circuit board and the secondhousing part. Retaining elements that are configured on the secondhousing part prevent the printed-circuit board, once it has arrived inits final position, from being pressed back into the hollow space by thecompressive force of the compressed sealing material, as a result ofwhich the sealing bulge would be pulled away from the housing walls. Onedisadvantage in such a device is that the printed-circuit board must beprovided with openings for the supporting elements, and therefore spaceis lost on the printed-circuit board for the arrangement of electricaland/or electronic components. In addition, electrical connecting leadscannot be fed into the housing interior through the bulge-like sealbetween the housing parts, and therefore must be fed, in a cumbersomemanner, through a separate passage in one of the two housing parts intothe housing interior. This passage also must be sealed off, requiringadditional expense. Harmful gases in the enclosed hollow space above theprinted-circuit board can impair the mode of functioning of theelectronic components on the printed-circuit board.

SUMMARY

As a result of the electrical device according to the present invention,the foregoing disadvantages that may arise may be avoided, and reliableprotection from harmful environmental influences is made possible for acircuit element arranged in a housing. The device assures a sufficientseal of the circuit element with respect to spray water, humidity, orsubmersion in water. The device is both simple as well as economical tomanufacture and has two half-shells, the interior area of which in eachcase is subdivided by interior walls into at least two chambers, ofwhich a first chamber is filled with sealing material, e.g., a gel, andhas spatial dimensions that are larger than the dimensions of thecircuit element. In the joined state of the two half-shells, theinterior walls of the second half-shell overlap, with clearance, theinner walls of the first half-shell, as a result of which it is achievedthat the sealing material contained in the two half-shells comes intocontact around the circuit element in a frame-like, circumferentialarea, merges together, and thus seals off the circuit elementcircumferentially. Due to tolerances in the housing dimensions,tolerances in the pouring of the sealing material, and a shrinkingprocess in response to the hardening of the sealing material, thesealing material poured into the first chambers before the assembly ofthe two half-shells forms a meniscus, so that the surface of the sealingmaterial in the two chambers is curved in a concave manner and contactsthe upper edges of the inner walls, although in the center of thechamber it recedes somewhat towards the interior. This may not beavoided in a simple manner and, without taking countermeasures, resultsin hollow spaces arising above and below the printed-circuit board whenthe two half-shells are joined together, due to the concave curvature.In order, when the two half-shells are joined together, to prevent afaulty seal of the edge area of the printed-circuit board from arisingas a result of an insufficient pressure of the sealing material in theedge area of the printed-circuit board, resulting from the presence ofthe hollow spaces, it is provided that the interior walls of the firsthalf-shell, when the two half-shells are joined, penetrate somewhat intothe first chamber of the second half-shell. As a result, it is achievedthat the first chambers of the half-shells, engaging one another, forman overlapping area, a sufficient quantity of sealing material beingpressed out of the overlapping area when the half-shells are joined inorder that the edge area of the circuit element be enveloped in sealingmaterial circumferentially in a sufficiently reliable manner. In thismanner, it may be achieved that the circuit element between the twohalf-shells is encased up to its electrical leads by the sealingmaterial contained in the two first chambers, i.e., it is arranged so asto be encapsulated in the sealing material.

Example embodiments and refinements of the present invention aredescribed below.

The interior area of each half-shell may be subdivided, by two interiorwalls, extending parallel to each other, which join to each other twoside walls of the half-shells facing each other, into a first chamberarranged centrally and two second chambers laterally adjoining the firstchamber. The second chambers provided in each half-shell function, interalia, as the receiving areas for excess sealing material that issqueezed out of the first chambers when the two half-shells are joinedtogether. As a result of the distance between the interior walls of thefirst and the second half-shells, a drainage channel is formed for thesealing material that is squeezed out of the first chambers, which isable to escape via the drainage channel into the second chambers.

The half-shells may be joined to each other, e.g., using a detentionarrangement. When the two half-shells are joined together, largerquantities of sealing material are compressed and are squeezed out ofthe overlapping area of the first chambers. Without a joiningarrangement, the strong compressive forces resulting from thecompression may force the two half-shells apart. The detentionarrangement may therefore be able to withstand larger forces. Thedetention arrangement, arranged on one half-shell, may include detenthooks having barbed-shaped latches, the hooks, in each case, engaging ina guide slot arranged on the other half-shell and which, in each case,gripping from behind, using their latches, a projecting part arranged inthe guide slot. The guide slots protect the latches, so that anunintentional unlatching of the latches is not possible. In particular,the width of each guide slot and the geometrical dimensions of thecorresponding latches may be adjusted to each other, so that a latchengaging in a barbed-like manner behind the projecting part may nolonger be detached from its latched position without being destroyed.

The side walls of the half-shells may have cutouts, which in the joinedstate of the housing part, form openings between the two half-shells forthe feeding through of the electrical connecting leads. When the twohalf-shells are joined, the connecting leads extending through theopenings to the outside are embedded in the sealing material.

A strain relief device may be provided on at least one half-shell forthe electrical connecting leads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an electrical device according tothe present invention.

FIG. 2 is a cross-sectional view of a segment of the electrical deviceillustrated in FIG. 1.

FIG. 3 is a perspective view of the second half-shell.

FIG. 4 is a perspective view of the first half-shell.

FIG. 5 is a top view of the first half-shell without the secondhalf-shell, having a circuit element placed onto the sealing material,and a foil conductor connected thereto.

DETAILED DESCRIPTION

FIG. 1 illustrates an electrical device for a system for occupantclassification in a motor vehicle. The device includes a housing 1, inwhich is arranged an electronic circuit element 4, for example, aprinted-circuit board having electrical and/or electronic components 7,8 arranged thereon. The printed-circuit board is connected via a foilconductor 6 to a seat mat for a vehicle seat, the seat mat having aplurality of local pressure-sensitive sensors. In addition, a wire 5 isprovided, which connects the electronic circuitry arranged on theprinted-circuit board to an airbag. The device makes it possible todetermine the passenger occupancy of a vehicle seat and the type ofpassenger (child or adult) and, as a function of the data ascertained inthis manner, to drive an airbag. The present invention, however, is notlimited in principle to the example embodiment illustrated but may alsobe used in other electrical devices which employ a circuit element thatis arranged in the interior of a housing and that may be protectedagainst environmental influences, such as humidity or harmful gases.

As illustrated in FIG. 1, housing 1 includes a first half-shell 2 and asecond half-shell 3. Both are made of plastic and contain, in the joinedstate, a housing interior space, in which printed-circuit board 4 isarranged. The half-shells, however, may also be made of a differentsuitable material, for example, metal. A perspective-view of theinterior area of the first half-shell is illustrated in FIG. 4, and aperspective view of the interior area of the second half-shell isillustrated in FIG. 3. As illustrated in FIG. 4, first half-shell 2 hasfour side walls 21, 22, 23, 24, and a base wall, on the interior side ofwhich a grating made of bars 41 is configured. Side walls 22 and 24,opposite each other, are linked to each other by two parallel interiorwalls 25, 26, which subdivide the interior area of first half-shell 2into a first chamber 20 and two second chambers 27 a and 27 b, laterallyadjoining. Essentially rectangular first chamber 20 is bordered by sidewalls 22 and 24 and interior walls 25 and 26. In addition, side wall 23has a U-shaped cutout 29, and side wall 21 has a C-shaped cutout 28. Oneach of the two side walls, 23, two detent hooks 44 are configured,which, parallel to side walls 21, 23, protrude from the upper edge ofthe side walls. In second chamber 27 b, arranged adjoining to cutout 29,two pegs 42 and 43 protrude into the interior area from the base offirst half-shell 2, the pegs functioning as a strain relief device for afoil conductor 6. In addition, the exterior edge of side walls 31, 32,33, 34 has a partially circumferential rib 60.

Second half-shell 3 is illustrated in FIG. 3 and is configured similarlyto first half-shell 2. It has four side walls 31, 32, 33, 34, and a basewall, on the interior side bars 51 of which are arranged in agrating-like manner. Side walls 32 and 34 are linked to each other bytwo interior walls 35 and 36, arranged parallel to each other. Sidewalls 32 and 34 and interior walls 35 and 36 border a centrally arrangedfirst chamber 30, which is separated by interior walls 35 and 36 fromtwo second chambers 37 a and 37 b, laterally adjoining. Side wall 33 hasa U-shaped cutout 39, and side wall 31 has a C-shaped cutout 38. Inaddition, four through guide slots 54, having a rectangular crosssection, are introduced into side walls 31 and 33 for detent hooks 44 offirst half-shell 2. Guide slots 54 extend parallel to side walls 31, 33and have at their ends in each case an opening 57, 58 (FIG. 2). Theexterior edge of side walls 21, 22, 23, 24 is provided with a partiallycircumferential groove 61, into which rib 60 of second half-shell 3engages when the two half-shells are joined together.

The length and width of first chamber 20 of first half-shell 2 and thelength and width of first chamber 30 of second half-shell 3 are in eachcase dimensioned larger than the length and width of printed-circuitboard 4. The distance between interior walls 35 and 36 of secondhalf-shell 3 is dimensioned larger than the distance between interiorwalls 25 and 26 of first half-shell 2.

When the device is manufactured, first, both first chambers 20 and 30are filled to the upper edge of the bordering interior walls and sidewalls with a fluid sealing material. The highly viscous sealing materialis made of, for example, a hardened gel. The gel may have a compositionas is described in European Published Patent Application No. 0 722 624.The gel, poured into chambers 20, 30, forms a surface that has a concavecurvature, the surface receding to the inside in the central area of thefirst chambers, towards the chamber base. Subsequently, as illustratedin FIG. 5, a printed-circuit board 4, which is provided with electricaland/or electronic components 7, 8, is placed onto gel filling 12 offirst chamber 29 of the first half-shell. Printed-circuit board 4 isjoined to a foil conductor 6 of the seat mat. Foil conductor 6 has twolayers of contact strips 6 a and 6 b, insulated from each other, whichin the end area are separated and are connected to corresponding contactsurfaces on the upper side and the lower side of circuit board 4, asillustrated in FIG. 2. As illustrated in FIG. 5, wire conductors 15 of aconnecting cable 5 are electrically connected to a connector 8 onprinted-circuit board 4 for driving an airbag. Cable conductors 15 maybe arranged in second chamber 27 a of first half-shell. Foil conductor 6has circular cutouts, through which pegs 42 and 43 penetrate, as aresult of which a strain relief device is formed for foil conductor 6.As illustrated in FIG. 5, the edge of printed-circuit board 4 isseparated from side walls 24 and 22 by a distance b of some millimetersand is separated from interior walls 25 and 26 by a distance a, also ofsome millimeters.

Subsequently, second half-shell 3 is placed onto first half-shell 2. Inthis context, four detent hooks 44 of first half-shell 2 penetratethrough openings 57 into guide slots 54 of second half-shell 3, asillustrated in FIG. 2. Because the distance between interior walls 35and 36 of second half-shell 3 is dimensioned larger than the distancebetween interior walls 25 and 26 of first half-shell 2, interior walls35 and 36 of second half-shell 3, in this context, are beyond interiorwalls 25 and 26 of first half-shell 2 by a distance d. When bothhalf-shells 2, 3 are brought into closer proximity, gel layers 12 and 13in both first chambers 20 and 30 come into contact in the edge area ofprinted-circuit board 4. As a result of further pressure, it is achievedthat interior walls 25, 26 of the first half-shell penetrate into firstchamber 30 of second half-shell 3 a certain distance c. Interior walls25, 26 of the first half-shell may penetrate some millimeters into firstchamber 30 of second half-shell 3. In this context, printed-circuitboard 4 is pressed into gel layer 13 of second half-shell 3. Gel layers12 and 13 are compressed and gel is squeezed out of the overlappingarea. The compressed gel is partially pressed, between set-apartinterior walls 25 and 35 and set-apart interior walls 26 and 36, intosecond chambers 27 a and 27 b of first half-shell 2. As a result of thepartial penetration of first chamber 20 of first half-shell 2, filledwith gel 12, into first chamber 30 of second half-shell 3, filled withgel 13, enough gel may be squeezed out to assure with sufficientcertainty that the printed-circuit board, having its electricalconnecting leads, is completely enveloped by gel, i.e., is encapsulatedin gel.

The quantity of displaced gel, in this context, may be adjusted throughparameters a, b, and c.

When both half-shells 2, 3 are joined together, C-shaped cutouts 28, 38form a circular opening for the feeding through of connecting lead 5.Conductors 15 of conducting lead 5 are brought into contact withconnector 8 through the gap between interior walls 25 and 35, and arecompletely enveloped by gel. U-shaped cutouts 29, 39 of both half-shells2, 3, in the joined state of the two half-shells 2, 3, form aslot-shaped opening, through which foil conductor 6 is conducted intosecond chambers 27 b, 37 b. From there, foil conductor 6 extends throughthe gap between interior walls 26 and 36 to printed-circuit board 4 andis enveloped on all.sides by the gel that is present.

When half-shells 2, 3 are joined together, detent hooks 44, insertedinto openings 57, slide into guide slots 54, spring back behindprojecting parts 55 in the guide slots, and in a barbed manner, lock in,using their latches 45, behind projecting parts 55, as illustrated inFIG. 2. Width e of guide slot 54, in this context, is dimensioned sothat assigned latch 45 may be conducted just barely between projectingpart 55, extending into the guide slot, and the inner wall of the guideslot, opposite the projecting part. It may be provided that wall 59 ofguide slot 54, provided with projecting part 55, in this context, may bebent in an elastic manner and springs back as soon as latch 45 passesprojecting part 55. It may be achieved, in this manner, that detenthooks 44 may not be released from their latched position without beingdestroyed. The depicted latch connections make possible a reliable andstable latch connection of the two half-shells 2, 3.

The present invention is not limited to the example embodimentillustrated. Modifications of the arrangement of the housing arepossible. For example, the interior walls do not necessarily have toextend parallel to each other. Thus it is possible, for example, to setoff the first chamber in each half-shell, for example, by circularinterior walls from a circular second chamber surrounding the firstchamber, or similar modifications. The interior walls of the secondhalf-shell may overlap the interior walls of the first half-shell withclearance, and the interior walls of the first half-shell may penetratesomewhat into the first chamber of the second half-shell. In addition,example embodiments are also possible in which, in place of the foilconductor, a further connecting lead is used, or the control deviceincluding only one connecting lead. In place of the gel, anothersuitable fluid sealing material may be used, which, when the twohalf-shells are pressed together, is partially squeezed out.

What is claimed is:
 1. An electrical device, comprising: two housingparts combinable into one closed housing, the housing parts, in a joinedstate, configured to enclose a housing interior space; an electricalcircuit element arranged in the housing interior space; and a sealingmaterial configured to protect the circuit element; wherein the twohousing parts are configured as half-shells, and an interior volume ofeach half-shell subdivided by interior walls into at least two chambers,a first chamber filled with the sealing material and having spatialdimensions larger than dimensions of the circuit element, the interiorwalls of a second half-shell, in the joined state of the twohalf-shells, configured to overlap, with a distance, the interior wallsof the first half-shell, the interior walls of the first half-shellconfigured to penetrate a distance into the first chamber of the secondhalf-shell, the circuit element between the two half-shells enveloped bythe sealing material contained in the two first chambers up toelectrical connections of the circuit element.
 2. The electrical deviceaccording to claim 1, wherein the interior area of each half-shell issubdivided into a centrally arranged first chamber and two secondchambers laterally adjoining the first chamber by two interior wallspositioned parallel to each other, the interior walls configured to jointwo side walls of the half-shells, the side walls opposite each other.3. The electrical device according to claim 1, wherein each half-shellincludes at least one second chamber configured as a receiving area forexcess sealing material squeezed out of the first chamber when the twohalf-shells are joined together, a discharge channel formed by thedistance between the interior walls of the first and second half-shells,the discharge channel configured to receive sealing material that issqueezed out of the first chambers.
 4. The electrical device accordingto claim 1, further comprising an arrangement configured to join thehalf-shells to each other.
 5. The electrical device according to claim4, wherein the arrangement includes detent hooks arranged on a first oneof the half-shells, each detent hook configured to engage a guide slotarranged on a second one of the half-shells, a latch of the hooksconfigured to grasp in barbed fashion a projecting part arranged in theguide slot.
 6. The electrical device according to claim 5, wherein awidth of each guide slot and geometrical dimensions of the correspondinglatch are adjusted to each other so that a latch engaged in a barbedmanner behind the projecting part is not releasable from a latchedposition without being destroyed.
 7. The electrical device according toclaim 1, wherein the side walls of the half-shells include cutouts that,in the joined state of the housing parts, form openings arranged betweenthe two half-shells, the openings configured to feed through electricalconnecting leads.
 8. The electrical device according to claim 1, whereinat least one half-shell includes a strain relief device adapted toelectrical connecting leads.
 9. The electrical device according to claim1, wherein the electrical connections include electrical connectingleads, the electrical connecting leads including an elastically flexiblefoil conductor.
 10. The electrical device according to claim 1, whereinthe sealing material includes a gel.
 11. The electrical device accordingto claim 2, wherein the two housing parts include a partiallycircumferential rib and a partially circumferential groove to engagewith the partially circumferential rib when the two housing parts arejoined.
 12. The electrical device according to claim 11, wherein thepartially circumferential rib is arranged on an exterior edge of sidewalls of the first half-shell, and the partially circumferential grooveis arranged on an exterior edge of side walls of the second half-shell.